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Hematocrit and hemoglobin levels are common blood tests used to assess the overall health status of patients as well as the oxygen-carrying capacity of the blood. The gold-standard technologies to determine the hematocrit and hemoglobin levels are precise and fast, but they are not pragmatic in extreme point-of-care settings due to the prohibitive cost, process complexity, and sophisticated facilities. Therefore, here, we report the development of a microfluidic paper-based analytical device to determine hematocrit and hemoglobin levels simultaneously. This device exploits the area of the stain formed by a spreading drop of 20 μl of whole blood on Whatman filter paper immobilized with sodium chloride and ethylenediaminetetraacetic acid for hematocrit level, whereas for hemoglobin concentration, it utilizes the gray color intensity of a 20 μl droplet of a mixture of blood and de-ionized water. The performance of the device is verified by comparing with gold-standard results of the automated hematology analyzer, showing a high degree of correlation (R2) of 0.9651 and 0.9701 for hematocrit and hemoglobin levels, respectively. The bias and standard deviation of the differences between the two measurements for hematocrit determination are 0.002 and 1.005, respectively, while the bias and standard deviation of differences between the two methods for hemoglobin determination are 0.065 and 0.398, respectively. This device is likely to provide a simple, fast, disposable, and inexpensive tool to determine the hematocrit and hemoglobin levels in resource-constraint settings. [ABSTRACT FROM AUTHOR]

Capillary wicking in a thicker gel blot microfluidics paper has been investigated through a combination of an analytical framework, experiments, and numerical simulations. The primary objectives of this work are to investigate the concentration-dependent wicking process inside thicker microfluidic paper and to estimate the concentration-dependent permeability using both theoretical models and experimental data. An additional goal is to estimate the parameters for saturation-dependent flow modeling in thicker microfluidic paper. To comprehend the wicking phenomenon on thicker gel blot paper, a series of experiments employing aqueous food dye solutions at varying concentrations has been conducted. In order to calculate the temporal wicking length analytically, the Brinkman-extended Darcy equation is implemented. By modifying the permeability expression for a simple rectangular unidirectional fiber cell and pure liquid, the expression of effective permeability for the analytical framework has also been introduced. The concentrations of the food dye solutions appear to have a substantial influence on the wicking phenomenon. Effective permeability and wicking length have been found to follow a decreasing pattern at lower concentrations while both increase at higher values. Intriguingly, employing a microfluidics paper with a relatively greater thickness facilitates the visualization of the fluid front. This phenomenon is identified by the formation of an acute angle at intermediate time instants, while the fluid front angle assumes an angle nearly ∼90° during smaller and higher time instants. In order to evaluate the saturation-dependent capillary pressure and permeability, the empirical correlation of concentration-dependent Brooks and Corey parameters is additionally determined experimentally. These parameters are subsequently employed in numerical simulations to illustrate the saturation-dependent flow field using Richards' equation. Furthermore, numerical simulations based on these estimated model parameters have been conducted, and it turns out that the saturation field has an excellent agreement with the experimental results. The results of the current study can be used to design low-cost paper-based diagnostic devices for usage in healthcare and environmental applications. [ABSTRACT FROM AUTHOR]

The search for efficient capillary pumping has led to two main directions for investigation: first, assembly of capillary channels to provide high capillary pressures, and second, imbibition in absorbing fibers or paper pads. In the case of open microfluidics (i.e., channels where the top boundary of the fluid is in contact with air instead of a solid wall), the coupling between capillary channels and paper pads unites the two approaches and provides enhanced capillary pumping. In this work, we investigate the coupling of capillary trees—networks of channels mimicking the branches of a tree—with paper pads placed at the extremities of the channels, mimicking the small capillary networks of leaves. It is shown that high velocities and flow rates (7 mm/s or 13.1 μl/s) for more than 30 s using 50% (v/v) isopropyl alcohol, which has a 3-fold increase in viscosity in comparison to water; 6.5 mm/s or 12.1 μl/s for more than 55 s with pentanol, which has a 3.75-fold increase in viscosity in comparison to water; and >3.5 mm/s or 6.5 μl/s for more than 150 s with nonanol, which has a 11-fold increase in viscosity in comparison to water, can be reached in the root channel, enabling higher sustained flow rates than that of capillary trees alone. [ABSTRACT FROM AUTHOR]

Transparent and nontransparent exoskeleton wearable heaters are used in automobile and aircraft deicing, oil-pipeline defrosting, smart windows, underwater protection clothing, winter sportswear, bioelectronics, personal healthcare, athletic rehabilitation, and thermotherapy applications. In this study, we introduce Korean traditional Han paper (or Hanji), which comprises eco-friendly cellulose fibers from the mulberry bark, as a substrate for nontransparent wearable heaters. Hanji consists of cellulose fibers and is highly flexible, making it suitable for low-cost roll-to-roll scalable production. Graphene flakes are readily and firmly embedded inside the fibrous structure of Hanji by the catastrophic impact inflicted by supersonic spraying. Additionally, Hanji can withstand temperatures of up to 100 °C before suffering thermal damage. The heater with the thicker graphene layer had the lowest electrical resistance and exhibited the highest heating temperature at a constant voltage level. Graphene flakes are firmly held inside the fibrous structure of Hanji, securing the material's mechanical durability. Additionally, tests at various bending radii were conducted to demonstrate the mechanical strength of the Hanji graphene heater. Graphene flakes deposited on an unyielding alumina substrate withstood temperatures of up to 280 °C, thereby facilitating the use of the substrate in high-temperature applications. Graphene-coated textiles were heated and stretched up to 50%, thus demonstrating the application of such materials in human-body thermotherapy. [ABSTRACT FROM AUTHOR]

In the present work, spontaneous imbibition of shear-dependent fluids is numerically investigated in a two-layered, rectangular/fan-shaped, paper-based diagnostic kit using the modified Richards equation. It is shown that the average velocity at the test line of the kit is strongly influenced by the absorbent pad's microstructure with its contact angle playing a predominant role. Assuming that the test fluid is shear-thinning, a generalized version of the Richards equation, valid for power-law fluids, was used to investigate the effect of shear-thinning on the quasi-steady regime. The shear-thinning behavior of the test fluid is predicted to shorten the duration of the constant-velocity regime on the nitrocellulose membrane used as the test cell. By manipulating the contact angle and/or choosing appropriate microstructure for the absorbent pad, it is still possible to establish a constant velocity regime at the test line for nearly five minutes even for such fluids. A comparison between our numerical results and published numerical results obtained using simplistic theories has revealed the key role played by the transition, partially saturated zone near the advancing front during the liquid imbibition. The general conclusion is that use should preferably be made of robust models such as Richards equation for the design of lateral-flow, paper-based assays. [ABSTRACT FROM AUTHOR]

The clogging or jamming of particle suspensions is a ubiquitous problem, hindering the efficiency of particle–liquid and particle–particle separations. Motivated by pressure screening in the pulp and paper industry, we characterize jamming of dilute and semi-dilute mono-disperse rigid-rod suspensions passing through channels mimicking dead-end and cross-flow filtration membranes, experimentally, using particle-tracking velocimetry. We observe that jams nucleate by either bridging of isolated particles across the constriction, or by localized mechanical entanglement of the particles, i.e., flocculation. Uniquely, we observe floc-formation during acceleration into the aperture and report this as primary mechanism for jamming events. We characterized the accumulation-release cycles of the jamming event using an exponential probability distribution; this distribution is indicative of a Poisson process. For jams nucleated by single-particle bridging, the distribution is (primarily) related to the number of fibers passing through the aperture; this is similar to dry, granular materials. For floc-based nucleation events, the distribution is (primarily) related to the suspension concentration with the average time between jams decreasing inversely with the square-root of the initial suspension concentration. For the conditions tested, the distribution was insensitive to changes in constriction geometry. [ABSTRACT FROM AUTHOR]

This study provides a complete rheological characterization of bidimensional (2D) nanomaterial dispersions, employed as 2D-inks precursors in printed electronics. Three different 2D nanomaterials [molybdenum disulfide (MoS2), graphene, and hexagonal boron nitride (hBN)] were dispersed in a Newtonian fluid (toluene) and a viscoelastic fluid (toluene + ethyl cellulose) with different polymer concentrations. The presence of nanosheets does not change the shear rheology of the carrier fluid. Regarding the extensional rheology, the results showed that the pinch-off phenomenon is present in all toluene suspensions; however, the presence of the ethyl cellulose introduces elasticity in the system, even leading to the formation of beads-on-a-string, and the relaxation times of the suspensions depend on the kind of nanosheets present in the fluid. As controlling the droplet size when dispensing 2D-inks is of paramount importance for printed electronics as well as for many other applications, here it is presented a correlation between the rheological properties of these 2D-inks precursors and their droplet size when generated from a capillary nozzle in the dripping regime. [ABSTRACT FROM AUTHOR]

The drainage properties of a gas diffusion layer (GDL) are essential factors in the performance of proton exchange membrane fuel cells. The GDL consisting of a three-dimensional (3D) carbon paper microstructure was developed and meshed with pore-scale reconstruction models in this paper. Localized binder and polytetrafluoroethylene (PTFE) structures were added to the carbon paper microstructure through 3D morphological imaging processing. The monitoring data of 1000 planes were multi-peaky fitted as a function of gas permeability and height to amend the macroscopic porous medium model. We analyzed drainage properties under different contact angles (θ) for the carbon paper with binder and PTFE. We described the mutual intrusion of moisture and air in GDL under different pressure differences. The results show that the pore-scale reconstruction model has the advantages of describing the flow in GDL accurately and with details, detecting low-flow resistance channels that spontaneously formed in GDL, and describing the variation of permeability as a function of location. In a hydrophobic environment, the liquid film connected to a GDL is challenging to split spontaneously. At the same time, the splitting motion of discrete droplets is more prominent than that of the liquid film. The pressure that enables complete water intrusion into the GDL is between 1 and 10 MPa. [ABSTRACT FROM AUTHOR]

Flat paper stained with water buckles and wrinkles as it swells and deforms out of the original plane. Here we quantify the geometry and mechanics of a strip of paper that swells when it imbibes water from a narrow capillary. Characterizing the hygroexpansive nature of paper shows that thickness-wise swelling is much faster than in-plane water imbibition, leading to a simple picture for the process by which the strip of paper bends out of the plane. We model the out-of-plane deformation using a quasi-static theory and show that our results are consistent with quantitative experiments. [ABSTRACT FROM AUTHOR]

A flow passing through a bluff body can produce Karman shedding vortex streets in its wake flow, resulting in strong unsteady loading and vibration. Existing passive control methods can disturb the wake flow, but are usually effective only under certain conditions and cannot adapt to changing environments due to their fixed topographies. Kirigami structures (the art of paper cutting) demonstrate programable out-of-plane buckling deformation under simple force actuations. By stretching and relaxing these kirigami sheets, an array of tilted surface elements can be easily activated and deactivated on the surface of a bluff body. For the first time, kirigami structures are used to achieve dynamic passive flow control. The control performance on the wake flow of a cylinder is validated in a wind tunnel using particle image velocimetry. Activated kirigami structures can push the shedding vortices further downstream from the cylinder by about four times of the uncontrolled one and reduce peak values of the turbulent intensity and Reynolds shear stress by 70% and 50%, respectively. The control performance is largely dependent on the height and shape of the kirigami structures. [ABSTRACT FROM AUTHOR]

Over the past few decades, there has been a significant increase in the use of paper-based microfluidic devices in various fields, including environmental monitoring, food safety analysis, and medical diagnostics. As a result, flow through paper-based substrates has gained much attention in the research community. Liquid flows through a paper substrate due to the inherent capillary suction pressure. In order to predict the flow through a paper substrate, we used macro- and microscopic methodologies to construct an analytical and numerical model. We have considered the effect of different factors, e.g., roughness, swelling, dynamic contact angle, and evaporation simultaneously to predict liquid wicking. A modified capillary radius technique is used to incorporate the effects of roughness and swelling into the numerical model, while a sink factor in Darcy's equation is used to model the evaporation. Experiments are performed to validate the developed models, and it is found that both models are in good agreement with the experiments, with a maximum error of 5%. The proposed analytical and numerical models can be used to forecast the capillary rise in a paper-based substrate, which has implications for paper-based microfluidic devices. [ABSTRACT FROM AUTHOR]

In Phys. Fluids 19, 118105 (2007), I. Lunati disputes my earlier paper [Phys. Fluids 18, 047102 (2006)], in which I pointed out an anomaly arising from Thomas Young’s concept of solid/fluid surface tension. The present article examines Lunati’s reasoning and concludes that my earlier paper is correct. [ABSTRACT FROM AUTHOR]

Yu I et al. i [1] presented an interesting investigation on the flow and aerodynamic heating characteristics of air and hydrogen-oxygen combustion gas under the same total temperature and pressure. The authors concentrated on the variations of temperature and velocity of the combustion gas flow in a nozzle and the shock standoff distance and stagnation pressure for the combustion gas flows around a sphere. Fluid mechanics covers a vast scope of flow phenomena that occur in nature, biology, and numerous engineering fields. [Extracted from the article]

A flexible sheet clamped at both ends and submitted to a permanent wind is unstable and propagates waves. Here, we experimentally study the selection of frequency and wavenumber as a function of the wind velocity. These quantities obey simple scaling laws, which are analytically derived from a linear stability analysis of the problem and which also involve a gravity-induced velocity scale. This approach allows us to collapse data obtained with sheets whose flexible rigidity is varied by two orders of magnitude. This principle may be applied in the future for energy harvesting. [ABSTRACT FROM AUTHOR]

In this Brief Communication, we examine in detail the motion of light particles—or dense gas bubbles—rising under gravity in a cellular flow. We follow the methodology of Maxey [Phys. Fluids 30, 1915 (1987)], and we examine a range of parameters not fully discussed in the past, corresponding to particles lighter and yet more inertial than the surrounding fluid if the added mass effect is considered. We observe a nonmonotonic behavior of the particle rise velocity, which exhibits a maximum for density of the particles only slightly smaller than the density of the fluid. The maximum value of the average rise velocity corresponding to the “optimum” density is several times (more than 40) higher than those obtained for small density changes around the optimum. The occurrence of this maximum is due to the combined effects of particle inertia and fluid added mass, which segregate the rising particles into specific, fast pathlines where the local fluid velocity adds to the particle gravitational velocity. A plot covering particle rise velocity for this range—not covered by the analysis of Maxey—is provided. [ABSTRACT FROM AUTHOR]

A previously developed lattice-Boltzmann lattice-spring method is applied to simulate a wet press process. In simulations, multi-individual flexible fibers are settled on a wire screen by the force of gravity, and a fiber network is formed on the top surface of the wire screen. Next, the coordinates and velocities of fluid and fiber solid particles are copied to a computer press simulator composed of two perforated plates. A pressure pulse is imposed at the fluid contact line of the two press plates. Water is squeezed out of the fiber network by the pressure. During simulations, fiber rigidity, fiber concentrations, and pressure pulses are varied and their effects on water removal and re-wet phenomena are systematically studied. [ABSTRACT FROM AUTHOR]

The unsteady behaviors of adiabatic effectiveness under oscillating flow conditions were studied extensively using the fast-response pressure-sensitive paint technique. Nitrogen was used as the coolant and was discharged from a 35°-inclined round hole. The oscillation frequencies of the mainstream were set to 0, 5, 10, and 20 Hz. The unsteady features of the measured effectiveness were quantified in terms of standard deviations, cross correlations, proper orthogonal decomposition (POD), and dynamic mode decomposition (DMD). Compared to the steady state, the measured effectiveness for the f = 10 and 20 Hz cases varied greatly during each cycle and led to significant enhancement in fluctuations. Cross correlations were used to determine the spatial signatures of large-scale structures (i.e., counterrotating vortex pairs, the horseshoe vortex, and structures near the hole) at various oscillation frequencies. Further POD and DMD analyses successfully decomposed the instantaneous fluctuations into a series of energetic modes, which vividly illustrated the strong modulations in adiabatic effectiveness imposed by flow oscillations and unsteady events. [ABSTRACT FROM AUTHOR]

In order to accurately predict the motion trajectory of ice shedding and ensure the safe flight of aircraft, the motion characteristics of ice shedding under two-dimensional (2D) and three-dimensional (3D) conditions are simulated and analyzed. Considering the influence of any possible shape of shedding ice and its rotation and the magnitude and direction of acceleration with time under aerodynamic force, a six degree-of-freedom analysis method is introduced in this paper. This paper proposes a theoretical model, which can be used to calculate the 3D trajectory of ice shedding with arbitrary shape. The dynamic analysis of real 3D shedding ice is carried out, and the motion behavior of shedding ice with different positions and shapes is calculated. The results show that the movement mode of the shedding ice after leaving the aircraft is translation and rotation. The shape of the low-speed region on the leeward side of the shedding ice will first increase, then decrease, and then increase with the rotation of the ice body. The influence of ice shape on ice shedding trajectory is mainly that the shedding ice continues to flip during the downstream movement of the flow field, and the projected area of the effective windward area in the lift and the drag direction changes with time. The average deviation of the shedding ice at position 5 along the spanwise is only 22.9% of that at position 1. Finally, the closer the initial position of ice shedding is to the airfoil root, the greater the probability of ice shedding hitting the aircraft fuselage. In this paper, the probability of ice shedding hitting the aircraft fuselage is 8%, which all occurred in the case with position 1 as the initial position of ice shedding. [ABSTRACT FROM AUTHOR]

Liquids spreading over a solid substrate under the action of various forces are known to exhibit a long wavelength contact line instability. We use an example of thermally driven spreading on a horizontal surface to study how the stability of the flow can be altered, or patterns selected, using feedback control. We show that thermal perturbations of certain spatial structure imposed behind the contact line and proportional to the deviation of the contact line from its mean position can completely suppress the instability. Due to the presence of mean flow and a spatially nonuniform nature of spreading liquid films the dynamics of disturbances is governed by a non-normal evolution operator, opening up a possibility of transient amplification and nonlinear instabilities. We show that in the case of thermal driving the non-normality can be significant, especially for small wave number disturbances, and trace the origin of transient amplification to a close alignment of a large group of eigenfunctions of the evolution operator. However, for values of noise likely to occur in experiments we find that the transient amplification is not sufficiently strong to either change the predictions of the linear stability analysis or invalidate the proposed control approach. [ABSTRACT FROM AUTHOR]

The flow around a cylinder near a free surface contains many physical phenomena and mechanisms, especially when the cylinder is moving. In this paper, the two-dimensional flow of a rotating cylinder near the free surface is simulated. The dynamic behavior of the rotating cylinder and the flow characteristics such as force coefficient, vortex structure, and air entrainment under different depth ratios, Fr numbers, and rotation ratios are discussed. In such problems, the rotational motion is rarely mentioned. The two-phase model is the sharp volume of the fluid method based on the two-dimensional incompressible Navier–Stokes equation. Combined with the spatially adaptive four-octree grid, the gas–liquid interface is reconstructed with the high-density ratio (ρwater/ρair = 816). The results show that, at α ≤ 2.0, the combined effect of the free surface and the rotation causes the wake vortex to produce a positive upper and negative lower distribution, which is contrary to the single condition. For the rotating cylinder, the existence of a free surface leads to the stable vortex layer at a low rotation ratio (α = 1.0), which only occurs at the high rotation ratio (2 < α < 4.2) without free surface. For the force coefficients, the simultaneous existence of the free surface and the rotation obviously changes the value and periodicity of the coefficients, which is different from the single condition. As for the air entrainment, it can be divided into two categories within the selected parameters: vortex entrainment caused by the parallel free surface and wake jet entrainment. In the latter model, the entailed bubbles have a wider distribution in space due to the influence of shedding vortices. [ABSTRACT FROM AUTHOR]

The wind shear layer is a naturally formed airflow that enables the albatross to soar for six days at almost no cost. The modeling and prediction of the wind shear layer can be very helpful for a long-endurance flight (dynamic soaring), but the existing studies usually ignore the turbulence structures of wind shear layers. In this paper, the wind shear layer on the leeward side of the ridge is simulated by a large eddy simulation (LES) method to analyze the turbulence structures. In the numerical simulation, the three-dimensional (3D) elevation data of the mountain is used as the topography at the bottom and the synthesized turbulent velocity is used as the inlet boundary. Because of the huge computational cost of 3D simulations, a data-driven predicting framework is also established to reduce the cost and maintain the prediction accuracy, which includes an offline training stage and an online forecasting stage. In the offline stage, the proper orthogonal decomposition (POD) is used to extract features from the LES data of wind velocity fields and the obtained POD coefficients are used to train the long short term memory (LSTM) networks. In the online stage, the future wind fields are predicted by the trained LSTM networks in the noisy and real-time environment. In conclusion, this paper analyzed the physical characteristics of the wind shear layer on the leeward side of the ridge and provided the accurate prediction for these characteristics. [ABSTRACT FROM AUTHOR]

This paper is a brief review of recent research on the streamwise corner boundary layer as it affects the component performance evaluation of both the theoretical and practical aircraft design. Typical examples include aircraft wing–body junction, rectangular air intakes, and turbine-hub flow. The paper addresses the questions of what we know and do not know about the streamwise corner boundary layer. Streamwise corner flows are characterized by the presence of secondary flows in the cross-stream planes, which are driven by the normal and secondary-shear components of the Reynolds stress tensor. Extensive studies of analysis for Prandtl's second kind of secondary flows have promoted the understanding of characteristics and formation of streamwise corner boundary layer. However, compared to the flat plate boundary layer, the research on the streamwise corner boundary layer is still far from enough, especially in the similarity solution, the instability, and transition mechanism. In recent years, a significant progress has been achieved in the study on the streamwise corner boundary layer in turbulent flow through direct numerical simulation and stress − ω Reynolds stress model. [ABSTRACT FROM AUTHOR]

When one brings a wet paintbrush into contact with a vertical watercolor paper, the paint may wick into the porous sheet completely or run down to ruin the art. We study a simple model of this spreading dynamics of liquids on hydrophilic porous sheets under the effects of gravity, using a capillary as a liquid source and thin fabrics of non-woven polyethylene terephthalate. Upon finding the maximum flow rate, Qw, that can be absorbed into the fabric, we show that the model can be used to obtain an estimate of the in-plane permeability of fabrics in a simpler manner than the conventional schemes. The shape of a wetting area that grows when the flow rate exceeds Qw to lead to rivulet formation is also theoretically given. The nose shape of the wetting front is shown to be time-invariant, while its profile depends on the properties of the liquid and the fabric. This study can be applied to understand and improve the liquid absorption behavior of hygiene items, heating, ventilation, and air-conditioning equipments, and fuel cell membranes in addition to elucidating the mundane painting activity. [ABSTRACT FROM AUTHOR]

This paper presents a metastructure device (MSD) modulated by liquid crystal (LC) and vanadium dioxide (VO2), suitable for circular-to-linear polarization conversion and refractive index (RI) sensing. The MSD employs a 2 × 2 array as a unit cell, forming a circular-to-linear polarization conversion. Filling the MSD with analytes of different RIs can cause changes in the electromagnetic properties of the MSD, thus realizing the sensing function. Furthermore, the detection range of the sensing can be modified by changing the long-axis pointing of the LC molecules under an applied voltage, resulting in multi-range detection. The RI unit is denoted as RIU. Without an applied voltage, the RI detection range is 1.949–2.607, with a sensitivity of 199 GHz/RIU; under full-bias conditions, the detection range is 2.828–3.391, with a sensitivity of 143 GHz/RIU. In the initial state of LCs, this paper also explores the use of the phase transition of VO2 to adjust the conductivity of VO2 to achieve changes in the detection range. In the insulating state, the detection range is 2.12–2.607, with a sensitivity of 225 GHz/RIU, while in the metallic state, the detection range is 1–2, with a sensitivity of 183 GHz/RIU. Furthermore, altering the thickness of the analyte also affects the electromagnetic properties of the device, causing a shift in the peak axial ratio frequency, making the MSD suitable for analyte thickness detection. The MSD has a wide detection range, high sensitivity, and adaptability, making it suitable for identifying cancer cells and giving a new method of monitoring human health. [ABSTRACT FROM AUTHOR]

The stress of surrounding rock and supporting structure is very complicated during the construction of a loose rock tunnel. The characteristics analysis of collapse arch is very important for the construction safety. This paper compares and analyzes the applicability of the full section method and the three-step method under shallow buried loose surrounding rock, reveals the influence law of tunnel excavation height span ratio on the stability of a pseudo-collapse arch of surrounding rock under shallow buried loose surrounding rock, and rationally chooses the three-step method as the dominant construction method of tunnel construction under this geological condition. For the three-step construction method, the optimization study of the excavation height of the upper step is carried out, the relationship between the excavation height of the tunnel and the stress concentration area under the condition of shallow buried loose surrounding rock is revealed, the influence of surrounding rock stress release on the stability of the tunnel surrounding rock is explored, and the damage of tunnel rock mass caused by the stress concentration phenomenon is analyzed. It is determined that the optimal excavation height of the upper step is 0.4H under the geological conditions of the DS project in Sichuan province, China, under construction. This paper analyzes the influence of structural plane spacing on the stability of a tunnel collapse arch under shallow buried loose conditions and reveals the law that the smaller the structural plane spacing, the worse the self-bearing capacity of the collapse arch, and the higher the risk of engineering accidents such as rock collapse or even collapse in the tunnel, which effectively guides the safe construction of the tunnel under shallow buried loose geological conditions. [ABSTRACT FROM AUTHOR]

The natural circulation loop is crucial for the safe and stable operation of nuclear reactors and other applications. Traditional numerical algorithms, based on the Boussinesq approximation, have limitations when dealing with large temperature differences and density disparity, and they do not fully address fluid compressibility. This paper adopts the decoupled and stabilized lattice Boltzmann method (DSLBM) with a non-Boussinesq algorithm to study the natural circulation loop. The DSLBM provides a detailed flow description under large temperature and density differences, incorporating the pseudopotential multiphase model, temperature equation, and state equation, without relying on assumptions. The study examines the loop's performance under various temperature differences, central height differences, and heating source lengths, focusing on mass flow rate, driving head, and heating power. It reveals the energy performance, flow characteristics, and heat transfer properties of the loop, highlighting the physical mechanisms involved. Comparison with the empirical formulation of the incompressible equation from the theoretical aspect shows that when the temperature difference coefficient is lower than 0.15, the two methods are not much different from each other. When the temperature difference coefficient reaches 0.2, 0.3, and 0.4, the difference between the two methods is 9.47%, 19.11%, and 42.64%, respectively. Consequently, the Boussinesq approximation can be compensated by DSLBM, which proves the value of the application of the algorithm in exploiting the compressibility of fluids. The dimensionless fitting correlation with greater universality is obtained, which helps to predict the properties of the natural circulation loop with varying temperature differences, friction coefficients, and geometric structures. The research in this paper will lay the foundation for optimizing the system design of the natural circulation loop and improving energy utilization efficiency. [ABSTRACT FROM AUTHOR]

Semi-local scales have been widely used in compressible wall-bounded turbulence, but it is still unclear whether they are applicable to the scaling of coherent structures, especially under conditions of high Mach number and cold wall temperature. By scrutinizing the direct numerical simulation dataset at different Mach numbers and wall temperatures, this paper demonstrates that the coherent structures normalized by semi-local scales are universal in size. In addition to this, we find that the ratios of Kolmogorov scales to semi-local scales are independent of Mach number and wall temperature. Thus, Kolmogorov scales can achieve the same scaling effect as the semi-local scales. The velocity spectra are also compared to verify the current scaling method quantitatively. A method to determine the threshold for the vortex identification criterion is proposed, allowing the same threshold for different cases to obtain vortices of similar size. The scaling of other statistics including turbulent kinetic energy, streamwise Reynolds normal stress, and root mean square of fluctuating vorticity is also investigated. A new velocity scale is proposed based on the total-stress-based transformation for mean streamwise velocity, which can collapse the profiles of these statistics more accurately than the semi-local velocity scale. The present paper demonstrates that through appropriate normalization, the structures and statistics of compressible turbulence become universal, reaffirming the validity of Morkovin's hypothesis even for the present high Mach number and cold wall cases. [ABSTRACT FROM AUTHOR]

In Paper I, we presented comprehensive three-dimensional, three-component (3D, 3C) mean velocity profiles obtained through magnetic resonance velocimetry (MRV) within a 37-pin wire-wrapped rod bundle, elucidating the primary flow dynamics in sodium-cooled fast reactors. Building on this foundation, in this paper, we meticulously examine transverse velocity, helicity, and streamlines around rods, focusing particularly on the wake region of the wire within interior and edge subchannels. Our analysis uncovers a repetitive vortex evolution pattern in the wake, characterized by vortices forming, growing, weakening, and dissipating at 60° intervals of wire angular position. Furthermore, we highlight the significant variation in the azimuthal velocity component near the wire's wake, elucidating the dominant influence of wire orientation. Additionally, we identify the periodicity of flow split factor variations, demonstrating their dependence on wire orientation in interior subchannels and the prevailing impact of edge swirling in edge subchannels. Overall, our quantitatively derived experimental results provide valuable insights into flow patterns within the rod bundle, offering essential information for optimizing reactor design and analysis. [ABSTRACT FROM AUTHOR]

As an underwater thruster, the pump-jet propulsor (PJP) exhibits low radiation noise but generates significant line spectral noise in the low-frequency band. In this paper, we equipped the PJP hub with two types of propeller boss cap fins (PBCF): one fixed and the other rotating with the rotor. The hybrid large eddy simulation and Reynolds-averaged Navier–Stokes method, along with the Ffowcs Williams-Hawkings (FW-H) equation, are employed to systematically analyze the hydrodynamics, exciting force, flow noise, and flow field of PJPs. The results indicate that the fixed PBCF improves the hydrodynamic performance and reduces the exiting force, raising the rotor's thrust coefficient by 9.22%–14.99%. The fixed PBCF also modifies the characteristics of line spectrum noise but causes an increase in the flow noise. The rotating PBCF increases the rotor's thrust coefficient by 2.03%–3.15%, decreasing both exciting force and line spectrum noise. For instance, at the advance coefficient of 0.8, its sound pressure level at the rotor frequency drops to 49.6%. Additionally, the rotating PBCF increases the pressure of the hub wake and effectively reduces the hub vortices' strengths. This paper provides a theoretical foundation for designing PJPs that enhance concealment and minimize vibrations and noise. [ABSTRACT FROM AUTHOR]

Porous graphene membranes (PGMs) have nanopores with single atomic thickness, which enables the precise and stable supply of ultralow flow rate gas below 10−14 Pa·m3·s−1. Different from a conventional channel, the surface diffusion (SD) process in PGM has become increasingly important and unique. However, the physical process and mathematical model of gas molecule transport in nanopores with single atomic thickness remain unclear. These inadequacies constrained the application of PGM in ultrasensitive leak detection. In this paper, the SD process in PGM was investigated using molecular dynamics simulation. A test rig was constructed to verify the simulation results. The nanopores in PGM were quantitatively characterized using a transmission electron microscope. Results show that a transfer region encircling the nanopores was identified, which plays a crucial role in the SD process. Furthermore, the physical model of SD process is described with a two-step model. Finally, a mathematical model of the SD process is established and validated. This paper provides nanoscale insights for an in-depth understanding of the SD process in PGM and promotes ultrasensitive leak detection technology. [ABSTRACT FROM AUTHOR]

Study of the engraving process is significant for interior ballistics. Due to the high transient and strong nonlinear characteristics of the engraving, research on the engraving mechanism is challenging. In this paper, based on the one-dimensional two-phase flow model of interior ballistics coupled with explicit dynamics software, finite element simulation of the engraving is carried out to obtain the changes of parameters during the engraving process, and the dynamic characteristics of the projectile engraving are discussed. By comparing the simulation results with the experimental data, the accuracy of the coupling method in this paper is verified. The relationship between the structural parameters of the sealing band and the extrusion resistance is revealed, and the influence of the extrusion resistance on the dynamic characteristics of the projectile is demonstrated. The simulation results can provide an essential reference for selecting a reasonable sealing band structure. [ABSTRACT FROM AUTHOR]

In a lagoon basin, the tidal prism is related to the section of its inlet by a simple monomial relationship [L. J. LeConte, "Discussion on the paper, 'notes on the improvement of river and harbor outlets in the United States,' by D. A. Watt." Trans. ASCE 55, 306–308 (1905); M. P. O'Brien, "Estuary tidal prism related to entrance areas," Civil Eng. 1(8), 738–739 (1931); and J. T. Jarrett, Tidal Prism - Inlet Area Relationships (Coastal Engineering Research Center, US Army Corps of Engineers, Fort Belvoir, VA, 1976)]. Although it is not dimensionally correct and there are sophisticated models in two or three dimensions, this relationship is widely used because of its simplicity. Having a simple relationship can be very important, especially when it is necessary to make quick, albeit approximate, evaluations. To maintain this simplicity, the same monomial relationship is often used in multi-inlet lagoons, even if the initial assumptions are not fully met. Another difficulty in applying a monomial relationship to a multi-inlet lagoon is the definition of the area of each basin. In this paper, we propose a simple Eulerian, hydrodynamic, one-dimensional approach based on the dynamic response of a nonlinear harmonic system and a harmonic analysis of the interaction between two basins in a lagoon system. With such an approach, the definition of the basin surface is overcome simply by working on topographic control basins. The study leads to the definition of a relatively simple relationship for the estimation of tidal prisms, while maintaining the flexibility of a monomial relationship. If the geometrical characteristics and the bottom friction of the inlet channel, the topographic surface of the basins and the amplitude of the tide in the open sea are known, this relationship can be used to estimate the tidal prism in individual basins. The application of this relationship to two-dimensional numerical cases and real multi-inlet lagoons shows good agreement with experimental data. [ABSTRACT FROM AUTHOR]

Severe weather conditions during windstorms may result in unavailability of traditional displacement monitoring techniques for civil structures such as supertall buildings. To address this challenge, this paper develops a long short-term memory model with a physics-informed loss function to initially estimate the missing strain responses of structures during typhoons. Subsequently, the missing or unmeasured displacements of structures during typhoons are reconstructed using the estimated missing strain responses and limited field measurements (i.e., acceleration and strain responses), employing a displacement reconstruction method. The proposed methodology is validated using field measurements on a 600 m supertall building during Typhoon Lionrock, demonstrating the effectiveness in accurately reconstructing the missing displacements of the supertall building under typhoon conditions. Finally, the missing displacements of the supertall building during Super Typhoon Saola are reconstructed, and the accuracy of the reconstructed displacements is verified. This paper aims to offer a novel method for displacement reconstructions of supertall buildings during windstorms based on limited monitoring information, enabling real-time structural integrity monitoring while reducing maintenance costs and downtime. [ABSTRACT FROM AUTHOR]

Due to mutual interference between various components, the transitional motion of fluid particles in the flow field of pump jet propulsion becomes more complex and variable. Additionally, the vortex structure at the wake can undergo severe contraction and deformation. To further improve the accuracy of predicting the hydrodynamic performance of pump jet propulsion, this paper proposes a time-varying, space-varying, and induced velocity-varying free wake numerical calculation model based on potential flow theory. A set of hydrodynamic performance prediction methods that consider the interference of the free wake model is also established. Furthermore, a velocity smoothing model based on time reversal is constructed based on the distribution pattern of numerical singularity points during the induced velocity calculation process, which enhances the robustness of the calculation program. By comparing and analyzing the numerical calculation results with experimental results, including pressure, circulation distribution, and hydrodynamic performance, the accuracy of the free wake model proposed in this paper is verified. The results also demonstrate that the free wake model proposed in this paper can effectively improve the prediction accuracy of the hydrodynamic performance of the pump jet propulsion. [ABSTRACT FROM AUTHOR]

Turbine vanes may be subjected to the deposition of particles such as dust from the external environment. The deposition could affect their aerodynamic and cooling performances. As an effective cooling method, the film cooling could alter the deposition. In this paper, the deposition experiments at ambient temperature were conducted by using atomized wax as the substitute for real particles to investigate the influence of film cooling hole shapes on the deposition for different blow ratios and angles of attack. The results indicate that within the range of blowing ratios in this paper, the deposition on the pressure surface of different hole shapes increases with increasing blowing ratio. Among them, the cylindrical model exhibits the most significant variation in deposition, for example, with a relative increase of 94% in deposition when the blowing ratio was increased from 2.0 to 2.5. The CONSOLE test model showed a relative increase of 60%, while the conical and fan-shaped test model exhibited a relative increase of 20%. The conical, CONSOLE, and fan-shaped film cooling holes can mitigate the influence of the blowing ratio on the deposition of particles. Within the range of angle of attack in this paper, the deposition on the pressure surfaces with different hole shapes increases with the increase in the absolute value of angle of attack. The cylindrical test model exhibits the most significant variation. The conical and fan-shaped holes can mitigate the influence of the angle of attack on the deposition of particles. [ABSTRACT FROM AUTHOR]

This paper describes part of an experimental study on shear-based spray formation. A laminar liquid jet was ejected inside co-annular non-swirling and swirling air streams. The aerodynamic Weber numbers (WeA) and swirl numbers (S) of the flow cases ranged from 256 to 1426 and from 0 to 3.9, respectively. The aim of this paper is to investigate how S and WeA influence the breakup of a central laminar liquid jet within the fiber-type atomization regime. High-speed shadowgraphy was utilized to visualize the spray behavior, while phase Doppler interferometry was utilized to measure the droplet size and velocity distributions. It was found that as S increases, atomization is improved in a way that the droplets are blown outward from the central axis of the nozzle. However, for some specific flow cases, the median droplet diameter (D) does not appear to be related to S. These specific flow cases are discussed in this work. For S ≥ 0.3 , the upward motion of droplets located at the central axis of the nozzle was observed, which was caused by recirculating air flows. In addition, it was found that when S increases to 2.5, recirculating air flows start to penetrate to the water exit, which momentarily stops portions of the central laminar water jets from exiting. This pattern will be called turn-off behavior in this report. In order to study the underlying mechanisms behind the turn-off behavior, proper orthogonal decomposition was performed on the shadowgrams. It was found that the timing of turn-off initiation is random. [ABSTRACT FROM AUTHOR]

This paper presents the first numerical evidence of an intermittency route to period-2 thermoacoustic instability in a subcritical single-element liquid rocket engine burning hydrogen peroxide/kerosene as we decrease the equivalence ratio (ϕ) from fuel-rich to fuel-lean. To achieve this, three-dimensional compressible large eddy simulation algorithms combined with the Euler–Lagrangian framework are used. A one-equation eddy sub-grid turbulence model with a partially stirred reactor sub-grid combustion model is employed to simulate the spray turbulent combustion process in a high-pressure liquid-fueled combustor based on open-source platform OpenFOAM. This paper focuses on examining the transition process of the dynamical states in the thermoacoustic system and the synchronization between multiple subsystems. The results indicate that, as the equivalence ratio reduces continuously (1.5 ≤ ϕ ≤ 0.5), the system dynamics shift from period-1 oscillations (ϕ = 1.5) to period-2 oscillations (ϕ = 0.5) via intermittency (1.3 ≤ ϕ ≤ 0.9). Under the equivalence ratio of 0.7 (ϕ = 0.7), a transient mode switching between period-1 and period-2 was also observed. The synchronization processes between the pressure and combustion subsystems in terms of phase-locking and frequency-locking are responsible for the emergence of complex dynamical states. The cycle snapshots analysis also provides more details on the synchronization processes between the pressure and the multiple subsystems, such as vortex dynamics, mixture fraction, and combustion heat release. In summary, this paper sheds light on the complex non-linear thermoacoustic oscillations and the underlying physical mechanisms related to the two-phase flow of spray combustion in liquid rocket engines using three-dimensional large eddy simulations, paving the way for developing passive or active control methods. [ABSTRACT FROM AUTHOR]

The continuous variable speed technology is a key technology in the development of pumped storage units. When the operating range of the rotation speed is widened, the unit's stable and safe operation range will be constrained by conditions, such as cavitation, hump, and power limit. This paper uses a traditional fixed-speed pumped storage station as the research object. Based on the complete characteristic curves of the unit, the modification hypothesis after the application of variable speed technology is carried out, and the preferred operation curve of the pump working condition is obtained. The improvement of the cavitation characteristics of the fixed speed unit by the variable speed technology is studied in this paper, and the problems in the prediction of cavitation of prototypes based on model tests are also analyzed. In this paper, the cavitation characteristics of the model and prototype of a pump turbine are analyzed using computational fluid dynamics simulation, with the initial cavitation coefficient as the basis for judging the cavitation. This paper points out that there is a deviation in the direct prediction of the cavitation characteristics of the prototype through the model test and provides a more accurate method to predict the cavitation limit range of variable speed units, which provides a reference for practical engineering. [ABSTRACT FROM AUTHOR]

Technology to launch objects into the air is essential for various applications. In this study, we propose a solid object launcher that pushes the object of centimeter-scale by the rapid liquid motion resulting from explosive vaporization due to electric discharge in water. In particular, by using the electric discharge in a trapezoid-shaped chamber, we demonstrate that a centimeter-scale L-shaped piece of paper with 0.92 mg mass can be launched with an initial velocity ∼4 m/s in the direction of an elevation angle of ∼50°, while a centimeter-scale paper airplane with 29.6 mg mass can be launched with the maximum velocity ∼2 m/s along a glass slide runway with an elevation angle of ∼45°. In addition, to clarify the mechanism of solid launching phenomena, we systematically carried out vertical launching experiments of the centimeter-scale solid object of 60–340 mg. Moreover, as a central design concept peculiar to the solid launching device, we demonstrate the importance of water-repellent treatment of the solid surface. In the future, our device might be used to provide object-shooting technology for hybrid manufacturing technology or to protect orchards from birds. [ABSTRACT FROM AUTHOR]

The "communication blackout" occurs during the reentry of hypersonic vehicles, that is, the electromagnetic wave cannot pass through the plasma sheath due to high electron density formed around the vehicle, which has drawn much attention but has not yet been solved. In this paper, a novel magnetic control approach is proposed, in which a periodic magnetic field is applied near the head of the aircraft. Based on the magnetohydrodynamic simulation, a low electron density channel across the plasma sheath of vehicle under the magnetic control is revealed for the first time, which probably make Ka-band electromagnetic wave pass through. We also find that the reason for the low electron density channel is the variation of the vortex structure in the plasma flow near the wall, by the electromagnetic force exerted on the flow. Furthermore, the optimal magnetic field frequency for generating the low electron density channel is obtained. These findings will be of significant benefit to the solutions for the communication blackout problems. [ABSTRACT FROM AUTHOR]

Recent studies by Fong et al. ["Finite roughness effect on modal growth of a hypersonic boundary layer," AIAA Paper No. 2012-1086, 2012; "Stabilization of hypersonic boundary layer waves using 2-D surface roughness," AIAA Paper No. 2013-2985, 2013; "Numerical simulation of roughness effect on the stability of a hypersonic boundary layer," Comput. Fluids 96, 350–367 (2014); and "Second mode suppression in hypersonic boundary layer by roughness: Design and experiments," AIAA J. 53, 1–6 (2015)] have shown that finite roughness can attenuate Mack's second mode instability when placed at the discrete mode synchronization location for two-dimensional planar flow over a flat plate. However, more practical hypersonic flows are non-planer conical flows, and the roughness effect phenomenon in conical flows has not been extensively investigated. For that reason, this investigation research the ability of finite roughness strips to attenuate the second mode instability on a Mach 8 straight blunt cone with a freestream unit Reynolds number of 9 585 000. Two roughness configurations are studied: a single roughness strip and an array of six sequential strips. N-factor calculations determine the second mode frequency most likely to lead to turbulent transition, and the linear stability theory is used to determine the mode's synchronization location. In the unsteady simulations of the roughness configurations, a blowing-suction actuator introduces an upstream broadband Gaussian pulse. Fourier decomposition of the pulse's history shows that the single roughness strip attenuates frequencies higher than 208 kHz while lower frequencies are amplified. Likewise, the roughness array exhibits similar results, attenuating frequencies higher than 164 kHz and amplifying lower frequencies downstream. The results show that both configurations can delay second mode instability growth on a hypersonic blunt cone and possibly delay turbulent transition. However, investigations of the roughness effect's behavior downstream of the roughness configurations show that disturbance growth resumes and becomes more destabilizing to the boundary layer. [ABSTRACT FROM AUTHOR]

Floating breakwaters are crucial for maintaining the safety and performance of marine structures in relatively deep water. At present, conventional floating breakwaters have limited capability of attenuating medium to long-period waves (with periods ranging from 6 to 10 s in this paper). To enhance the performance of attenuating medium to long waves, a new floating breakwater with openings, arc-shaped wings, and plates is proposed in the present paper. Model experiments were carried out to analyze its wave attenuation performance and hydrodynamic characteristics. Comparative tests were also conducted on its prototype with opening passes and wing structures. The experimental results demonstrate that this new floating breakwater exhibits superior performance in attenuating medium to long waves compared to its prototype. However, this improvement comes at the cost of intensifying localized wave slamming and increasing mooring forces to a certain extent. [ABSTRACT FROM AUTHOR]

With the deep development of underground rock engineering, the threat of rock burst disasters is increasing. At present, the identification and prediction of rock burst mostly rely on the experience of field staff to determine the critical value and development trend, and there is a lack of efficient and intelligent methods for the utilization of massive data. Therefore, this paper constructs a rock burst signal recognition and prediction model based on deep learning methods to solve the above problems. In this paper, the acoustic emission (AE) and electromagnetic radiation (EMR) data of the site are first marked and input into the long-short-term memory-fully connected neural network model to realize the identification of rock burst danger signals. Then, the graph data of the AE and EMR sensor monitoring networks are constructed and input into the spatiotemporal graph convolutional network signal prediction model to predict future monitoring data. Finally, this paper uses the same dataset to compare and analyze several other commonly used deep learning models. The results show that the model constructed in this paper has the best performance in the identification and prediction of AE and EMR signals with rockburst risk. This study can provide theoretical reference for intelligent monitoring and early warning of rock burst in underground rock engineering. [ABSTRACT FROM AUTHOR]